class StringKumi
{
  
  private int i,j;
  private int it,jt;
  private char []mojis;
  private int length;
  
  public StringKumi(String str)
    {
      i = 0;
      j = 0;
      it = 0;
      jt = 0;
      
      mojis = new char[str.length()+1];
      for(int i= 0;i < str.length();i++)
        {
          mojis[i]  = str.charAt(i);
        }
      length = str.length();
    }

  private int getLength()
    {
      return this.length;
    }

  public String push_top()
    {
      int len = getLength();
      if( jt < len)
        {
          jt++;
        }
      else
        {
          return null;
        }
      return new String(mojis,0,jt);
    }
  
  public String  push()
    {
      int len = getLength();
      if(j < len){
        j++;
      }else{
        if(i < len){
          i++;
          j = i;
        }else{
          return null;
        }
      }
      return new String(mojis,i,j-i);
    }

  public static void main(String args[])
    {
      StringKumi test = new StringKumi("mosskite");
      for(String A = test.push();A!=null;A = test.push())
        {
      System.out.println(A);
        }
      System.out.println(test.push());
    }
  
}